Planet X Brake centering issue

Discuss light weight issues concerning road bikes & parts.
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doomith
Posts: 58
Joined: Fri Nov 09, 2012 4:57 am

by doomith

Hi there,

Have just built a new bike and have Planet X Ultralight brakes, the stopping power is fine and I really love them. Also as a note, using Yokozuna cables and housing, the housing being very stiff.

Have had them set up by a bike mechanic (i'm not one) and they worked fine for the first few rides.

I know this has been asked previously but I couldn't seem to find any examples where someone had the same problem as me.

Occasionally, after pulling on the brakes, one of the brake pads doesn't get pushed back far enough and the pad starts to rub on the rim.
This is not due to wheel flex etc. The first time it happened it was pressed so hard against the rim the wheel isn't able to spin.

I got the caliper tightened but the problem still exists, this time it seems that the brake pads rub a little, however is very noticeable.

One of my friends mentioned that he thought that housing might either be too short or too long.
Does anyone else who has used / installed these brakes have any input?
It's just frustrating as it's not every single time I use the brakes, only happens occasionally.

Beancouter
Posts: 380
Joined: Fri Apr 20, 2012 9:04 pm

by Beancouter

If you do a search there is a recent threat on this subject.

by Weenie


doomith
Posts: 58
Joined: Fri Nov 09, 2012 4:57 am

by doomith

Like a bomb threat ;)?
Okay will do, I her performed searches for this issue, but couldn't find anyone that had the same problem as me.

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btompkins0112
Posts: 2693
Joined: Fri Feb 11, 2011 3:04 am
Location: Mississippi

by btompkins0112

Adjust cable housing....if the housing is "pushing" the NDS pad into the rim, shorten the housing. If the housing is "pulling" the DS pad into the rim, cut a longer housing. Solved.

doomith
Posts: 58
Joined: Fri Nov 09, 2012 4:57 am

by doomith

Thanks mate - I managed to find the other thread that beancounter was referencing to. Looks good :)

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Rick
Posts: 2015
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

If the brake fixing bolt is snug, it will resist forces that tend to de-center.
But if the cable housing is the wrong length, it will tend to push (or pull) it off center. So both should be checked for proper installation.

by Weenie


MarkMcM
Posts: 96
Joined: Fri Mar 26, 2010 4:24 pm

by MarkMcM

Planet X brakes are single pivot brakes. Like all single pivot brakes, they rely on separate springs to retract each arm independently. Sometimes the springs do not exert the same force. Sometimes there are different amounts of friction on each arm. Sometimes the cable stiffness exerts unbalanced forces on the arms. Addressing any of these may help keep them centered.

Technical note:

Traditional single pivot brakes have lower mechanical advantage than either dual pivot brakes or leverage enhanced single pivot brakes (like the Planet X). The lower leverage allowed for larger pad-to-rim clearances, which in turn made these brakes less sensitive to variations in arm retraction forces.

Dual pivot brakes have additional linkages, which result in the arms retracting in unison. Once centered, the arms will always retract uniformly. (Due to the linkage, dual pivot brakes only require one spring to retract both arms.) The centering linakge allows dual pivot brakes to have higher leverage and lower pad-to-rim clearance, without the problem of pads dragging.

Leverage enhanced single pivot brakes can be lighter than dual pivot brakes, but the reduced pad-to-rim clearance makes them more sensitive to non-uniform arm retraction. These brakes must be set-up more carefully, paying closer attention to initial centering and cable length/stiffness, and are more prone to go out of centering adjustment in use. As they say, you can't get something for noting.

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